Whether you call it a thermos flask, a food flask or an insulated food jar, the concept is the same, it’s a wide mouth double wall vacuum insulated stainless steel container with a screw lid to keep hot food warm over a period of several hours or cold food chilled for a set period of time. It’s the food equivalent of an insulated water bottle. Most people use them to keep food warm, but they’re just as useful for keeping food chilled until you’re ready to eat.

Avanti provides hot insulation for up to 7 hours and cold insulation up to 9 hours. It is only 8.5cm in diameter. The inside of the lid is stainless steel so there's no plastic touching your food. Stainless steel is naturally non toxic and bpa free. They are also the best priced food jars in the range.

The Klean Kanteen TKCanister comes in 3 sizes and does hot insulation for up to 11 hours depending on the size. The larger food flask sizes provide better insulation in this brand, but they only provide this insulation when they’re pre-heated and full, which we explain in greater detail just below. They are easy to open & close with the handle and only need a quarter turn to lock them into place. The inside of the lid is silicone and can be removed for easy cleaning. There is no plastic touching the food. The silicone on the inside of the lid is naturally bpa free and highly resistant to retaining smells from food, but they can be easily removed by soaking in a solution of water and white vinegar when cleaning..

How do you get the best hot insulation performance out of a food flask?

For best hot results, pre-warm your food flask with hot water straight out of the kettle. Let the stainless steel heat up for a few minutes, tip out the water, add hot food in and FILL it. Without filling it or pre-heating, you won't get the full performance out of your stainless steel insulated food jar. At the end of the insulation period, you can expect your food to be still holding around half of the original heat when you put it in as long as the lid hasn't been repeatedly opened and you did fill and pre-heat it. Regardless of brand, this is industry standard expectations. Choosing a food flask for your meal that is rated past the time you want to keep your food hot for will give you better performance.

How do you get the best cold insulation performance out of a food flask?

Lid off, place the insulated food jar in the fridge to allow the stainless steel surface of the inside to cool to the touch a little. If you put it in the fridge with the lid on, the lid and the double wall insulation will protect the inside from the cold of the fridge and won’t change the temperature at all. You could also fill it with ice and a little water to chill it down. Add your food in cold and then place the lid on. The fuller it is, the better the insulation will work.